1316.  In that case the application of the instrument to very extensive research is evident.  Comparatively small masses of dielectrics could be examined, as diamonds and crystals.  An expectation, that the specific inductive capacity of crystals will vary in different directions, according as the lines of inductive force (1304.) are parallel to, or in other positions in relation to the axes of the crystals, can be tested[A]:  I purpose that these and many other thoughts which arise respecting specific inductive action and the polarity of the particles of dielectric matter, shall be put to the proof as soon as I can find time.

  [A] Refer for this investigation to 1680-1698.—­Dec. 1838.

1317.  Hoping that this apparatus will form an instrument of considerable use, I beg to propose for it (at the suggestion of a friend) the name of Differential Inductometer.

Royal Institution, March 29, 1838.

TWELFTH SERIES.

S 18. On Induction (continued). P vii. Conduction, or conductive discharge. P viii. Electrolytic discharge. P ix. Disruptive discharge—­Insulation—­Spark—­Brush—­Difference of discharge at the positive and negative surfaces of conductors.

Received January 11,—­Read February 8, 1838.

1318.  I Proceed now, according to my promise, to examine, by the great facts of electrical science, that theory of induction which I have ventured to put forth (1165. 1295. &c.).  The principle of induction is so universal that it pervades all electrical phenomena; but the general case which I purpose at present to go into consists of insulation traced into and terminating with discharge, with the accompanying effects.  This case includes the various modes of discharge, and also the condition and characters of a current; the elements of magnetic action being amongst the latter.  I shall necessarily have occasion to speak theoretically, and even hypothetically; and though these papers profess to be experimental researches, I hope that, considering the facts and investigations contained in the last series in support of the particular view advanced, I shall not be considered as taking too much liberty on the present occasion, or as departing too far from the character which they ought to have, especially as I shall use every opportunity which presents itself of returning to that strong test of truth, experiment.

1319.  Induction has as yet been considered in these papers only in cases of insulation; opposed to insulation is discharge.  The action or effect which may be expressed by the general term discharge, may take place, as far as we are aware at present, in several modes.  Thus, that which is called simply conduction involves no chemical action, and apparently no displacement of the particles concerned.  A second mode may be called electrolytic discharge; in it chemical